The field of the invention is in the capacitance measuring art.
Meters and instruments for measuring the capacity of capacitors are well known. The combination of an oscillator and a counter wherein the frequency of the oscillator is a function of the unknown capacitance and the counter counts cycles per unit of time; or the combination wherein the frequency of the osicillator is fixed and the number of cycles is counted that appear in a time gate, the length of which is a function of the unknown capacitor are well known. There are always stray capacitances in the measurement. These stray capacitances exist in the control circuits of the measuring device, in the leads or connections to the unknown capacitor, and in various capacitances to ground. Some capacitance measuring devices attempt to compensate for stray capacitances with a fixed amount of calculated or empirically determined balancing capacity. Frequently the unknown capacitor whose capacitance magnitude is desired is physically located in a structure such that it is not desirable to remove it and connect it to the measuring device in a determined manner, but must be connected to the measuring device with test leads of some description, with unknown and indetermined amounts of stray capacitances. In these instances the conventional measurements of capacitances are substantially only approximations.
The best known prior art may be found in the following U.S. Pat. Nos.: 3,761,805 to patentee Dornberger; 3,805,149 to patentee Delapierre; 3,882,380 to patentee Black; and 4,001,813 to patentee Kosakowski.